Mercy comes from the Latin merces, meaning "reward" or "pity." English Puritans adopted Mercy as a virtue name in the 17th century alongside Faith, Hope, and Charity.
Mercy is rising in the U.S.
Mercy does not currently appear in the US Social Security Administration's top 1,000 girls' names, so we don't publish a US rank or birth count for it. That says nothing about the name's standing elsewhere in the world — only that it sits outside the ranked US data we rely on.
In Pythagorean numerology the letters of Mercy reduce to 1, The Leader. This is a traditional interpretive system, not a factual claim about the name.